The present invention relates to an improved process for the liquefaction of raw coal. More particularly, the invention relates to a coal liquefaction process in which physical solids separation such as filtration or centrifugation may be replaced by distillation while still maintaining the recovery of high quality heavy distillate.
In any coal liquefaction process, the liquid product (coal-derived liquid) is a viscous slurry having a very complex chemical composition which includes a significant portion of solids such as ash, char and refractory organic compounds. The solids must be separated at some stage in the liquefaction process to prevent scaling, plugging and fouling of downstream equipment and to remove heteroatom contaminants and ash from the final product. Because a sizable percentage of the solid content of coal-derived liquids is in the micron to sub-micron size range, the problem of separating fine ash, char and refractory solids from unfiltered coal-derived liquids is a most difficult problem.
The present invention provides a method of separating solids from a coal-derived liquid which is particularly useful in a high-severity coal liquefaction process. The present invention also provides a means for eliminating such solids separation steps as filtration or centrifugation.